1. Field of the Invention
The present invention relates to a pulse width distortion correction circuit in a digital transmission system.
2. Description of the Background
Conventionally, as the circuit of the kind described above, there has been known the circuit shown in FIG. 6. In FIG. 6, the circuit has a signal input terminal 1 and a delay circuit 19 for delaying an input signal applied to the signal input terminal 1 so as output a signal delayed by a time T.sub.d. An AND gate 20 ANDs the output signal of the delay circuit 19 and the undelayed input signal applied to the signal input terminal 1 and supplies the result to a signal output terminal 4.
Next, the operation of the circuit of FIG. 6 will be described. Assume now that in FIG. 7, a signal (a) transmitted from a transmitter is received as a signal (b) which is prolonged by the time T.sub.d at its high level (or shortened by the time T.sub.d at its low level) due to distortion in pulse width through a transmission line. An example of such a transmission line is a light transmission line including electro-photo conversion and photo-electric conversion.
The signal (b) applied to the signal input terminal 1 is delayed by the delay circuit 2 by the time T.sub.d to be a delayed signal (c). The undelayed signal (b) and the delayed signal (c) are ANDed by the AND gate 3 so that a signal (d) is obtained at the signal output terminal 4.
Being arranged in a manner as described above, the conventional pulse width distortion correction circuit has a problem in that the correction can be achieved only in a case of specific pulse width distortion. If the pulse width distortion is changed by the condition of the transmission line or the like, not only can the correction not be achieved but conversely the pulse width distortion increases.